1. Field of the Invention
The present invention relates to a method and apparatus for washing with a washing solution a substrate such as a semiconductor wafer or a glass substrate for a liquid crystal display (LCD) device and to a method and apparatus for washing-drying such a substrate.
2. Description of the Related Art
In the initial process of manufacturing a semiconductor device, a semiconductor wafer used as a substrate is dipped in a chemical solution so as to remove foreign substances such as particles, organic contaminants, and metal impurities from the surface of the substrate, followed by water wash with a rinsing solution and, then, drying. A wet type washing-drying system is used for performing a series of these treatments.
The wet type washing-drying system comprises a wet station prepared by arranging in series a plurality of processing vessels. In the wet station, the substrate such as a semiconductor wafer is washed with various chemical solutions such as an ammonia-hydrogen peroxide solution, a hydrofluoric acid solution, a dilute sulfuric acid solution and a dilute hydrochloric acid solution, followed by washing with water and, then, by drying. Since a plurality of processing vessels are arranged in series, a plurality of wafers are successively dipped in different chemical solutions housed in the processing vessels so as to perform the washing-drying treatments efficiently.
Japanese Patent Publication (Kokoku) No. 6-82647 discloses a closed drying apparatus in which an isopropyl alcohol (IPA) vapor is used for drying wafers after the washing treatments. This prior art teaches that a pure water film is removed from the wafer surface when IPA is evaporated, making it possible to dry the wafer clean without generating a water mark on the wafer surface. In the drying apparatus of this type, however, the wafer is moved within the air atmosphere when transferred between the washing section and the drying section. It follows that the wet wafer is kept in contact with the air for a long time, with the result that foreign substances such as particles are likely to be attached to the wafer surface.
Further, Japanese Patent Publication (Kokoku) No. 6-103686 discloses another type of drying apparatus. In this apparatus, an IPA vapor is supplied to a process chamber while discharging a pure water from the process chamber so as to fill the process chamber with the IPA vapor.
Still further, European Patent No. 03 85 536 B1 discloses a wafer drying apparatus utilizing Marangoni effect. In this apparatus, wafers are dried while being pulled out of a pure water.
It should be noted that IPA has such a high boiling temperature as 82.degree. C., with the result that evaporation of the washing solution (pure water) is promoted. It follows that dews of pure water or IPA are formed on the inner surface of the chamber. The presence of the dews causes the purging time with a nitrogen gas, which is performed for bringing the atmosphere within the chamber back to the initial state, to be prolonged, leading to a low through-put. Further, the dews are likely to be evaporated again when the inner pressure of the chamber is lowered, with the result that the evaporated water or IPA is attached to the wafer W to form dews. It follows that water marks are likely to be formed on the wafer W. What should also be noted that, if the dew of water formed on the inner surface of the ceiling of the chamber drops onto the wafer W, the wafer W incurs a serious contamination. Still further, the dew of IPA is discharged without being dried, leading to waste of IPA.